Variable speed constant frequency power system with auxiliary DC output

Abstract

A DC-link, variable speed constant frequency power system is provided with an auxiliary DC output. The system includes a variable speed generator for producing a DC voltage on a pair of DC-link conductors. When the generator is operated in its normal speed range, an inverter converts the DC voltage to a constant frequency AC voltage. When the generator is operated at a speed which is below its normal speed range or when an external auxiliary output command signal is received, the DC-link conductors are switched to an auxiliary output line and the DC-link voltage is regulated to maintain the desired auxiliary output voltage level.

What is claimed is: 
     
       1. A DC-link, variable speed constant frequency power supply, having an auxiliary DC output, comprising: an electrical generator for producing a DC voltage on a pair of DC-link conductors;   means for regulating said DC voltage at alternative voltage levels by controlling the output of said generator;   an inverter for converting said DC voltage to a constant frequency AC voltage, when said DC voltage is at a first one of said voltage levels; and   means for switching a first one of said DC-link conductors to an auxiliary DC output line and for switching the other one of said DC-link conductors to a reference terminal, when said DC voltage is at a second one of said voltage levels.   
     
     
       2. A power supply as recited in claim 1, further comprising: means for disabling said inverter when said first DC-link conductor is switched to said DC-output line.   
     
     
       3. A power supply as recited in claim 1, wherein said means for switching comprises: a relay having an actuating coil and two pairs of contacts, wherein a first one of said pairs of contacts makes contact between said first DC-link conductor and said output line, and the other pair of contacts makes contact between the other one of said DC-link conductors and said reference terminal.   
     
     
       4. A power supply as recited in claim 3, wherein said first pair of contacts alternatively makes contact between said first DC-link conductor and a first input to said inverter and said second pair of contacts alternatively makes contact between said other one of said DC-link conductors and a second input to said inverter. 
     
     
       5. A power supply as recited in claim 1, wherein said means for regulating said DC voltage maintains said DC voltage at said first level when said generator is driven at a speed which is above a predetermined speed and maintains said DC voltage at said second level when said generator is driven at a speed which is below said predetermined speed. 
     
     
       6. A power supply as recited in claim 1, wherein said means for regulating said DC voltage includes: a first set of inputs connected to receive the AC output voltage of said inverter; and   a second set of inputs connected to receive the DC voltage on said DC-link conductors.   
     
     
       7. A power supply as recited in claim 1, wherein said means for regulating said DC voltage includes means for receiving an external auxiliary command signal such that when said external auxiliary command signal is received, said means for regulating said DC voltage maintains said DC voltage at said second level and in the absence of said external auxiliary command signal, said means for regulating said DC voltage maintains said DC voltage at said first level. 
     
     
       8. A method of operating a DC-link, variable speed constant frequency power supply having a generator which supplies DC power to an inverter via a pair of DC link conductors, said method comprising the steps of: controlling the generator output voltage to produce a first DC voltage between said DC-link conductors in the absence of an auxiliary output command signal;   controlling the generator output voltage to produce a second DC voltage between said DC-link conductors in response to an auxiliary output command signal; and   switching one of said DC-link conductors to an auxiliary output terminal while switching the other DC-link conductor to a reference terminal in response to said auxiliary output command signal.   
     
     
       9. The method of claim 8, further comprising the step of: disabling the inverter in response to said auxiliary output command signal.   
     
     
       10. A method of supplying auxiliary DC power from a DC-link, variable speed constant frequency power supply having a generator which supplies DC power to an inverter via a pair of DC-link conductors, said method comprising the steps of: monitoring the speed of the generator;   connecting one of the DC-link conductors to an auxiliary output line and connecting the other DC-link conductor to a reference point when the speed of the generator is below a predetermined speed; and   regulating the voltage between said DC-link conductors to maintain a predetermined auxiliary voltage level when the speed of the generator is below said predetermined speed.   
     
     
       11. The method of claim 10, further comprising the step of: disabling the inverter when the speed of the generator is below said predetermined speed.